3. Since the D depends on the velocity (decreasing all the time), the acceleration (-D/m)(make up your own m) is variable. Does this mean I can't use the suvat equations?

Any ideas guys?

Cheers,
Josh

Indeed, SUVAT equations are only valid when the acceleration is constant. What you really have is a first order differential equation for velocity. However, since you're after the stopping distance what you really really have is a second order differential equation in displacement. Both are non-linear equations, but luckily for you they have solutions in terms of elementary functions (which isn't generally the case for non-linear DEs). So, the equation you need to solve is

Although this is a good exercise in the solution of the DE, I think it is a trick question. I will explain my logic (as to why the plane mathematically never stops) if it would not interfere with the flow of the thread.

Although this is a good exercise in the solution of the DE, I think it is a trick question. I will explain my logic (as to why the plane mathematically never stops) if it would not interfere with the flow of the thread.

Yep, I've just realised this too. Of course, in reality, wheel braking force will also slow the plane down, and this isn't (easily) related to the velocity (like drag is).